The present invention relates to a device for converting a series of bits of the NRZ (nonreturn to zero) type into the CMI (code mark inversion) code, more particularly to a device for converting a series of bits of the NRZ type into the CMI (Class II) code by limiting the pulse size of said CMI code to the clock pulse cycle corresponding to the NRZ data-transmitting rate.
The CMI code is widely used in optical transmission systems in which the bit-transmitting rate is about 150 Mbps. This is because encoder and decoder for the CMI code have a relatively simple constitution, because the recovery of bit clock at the receiving terminal is easily carried out, because of bit transition of a series of the CMI code data, and because any error can be monitored on line by using the characteristics of code itself without any use of additional bits. However, conventional CMI (Class II) (hereinafter, referred to a CMI (II)) encorders have a complex constitution, as compared with the CMI (I) encorder. In addition, it is difficult to maintain an accurate duty cycle of the CMI code pulse. As a result, it is very difficult to practically use the system utilizing the CMI (II) code, in spite of several advantages obtained therefrom.